Present day telecommunications technology utilizes, to an increasing extent, optical fibers for signal transmission. The use of optical fibers, in turn, requires numerous collateral components especially adapted to handle the light or optical transmission, among which are optical fiber connectors, which are essential to virtually all optical fiber systems. Connectors may be used to join segments of fibers together to create longer lengths; to connect a fiber or fibers to active devices forming part of the communication system such as radiation sources, detectors, amplifiers, repeaters, or the like; or to connect the fibers to various types of passive devices such as switches, dividers, or attenuators. It is highly desirable, if not necessary, that the connectors perform their function with a minimum of signal loss, and that the making of a connection be as simple and as quickly accomplished as possible. The central function of an optical fiber connector or connectors, which most often are in butting relationship, is the positioning and maintenance of two optical fiber ends so that their central cores are aligned and in contact with each other, thus insuring maximum transfer of optical signals from one fiber to the other. Achieving this desideratum is a particularly challenging task inasmuch as the light carrying region (the core) of an optical fiber is quite small, being on the order of eight microns (8 .mu.m) diameter for single mode fiber. Another function of an optical fiber connector is to provide mechanical stability and protection of the actual connection in the working environment. Achieving maximum signal transfer (minimum insertion loss) is a function of the alignment of the fiber cores, the width of the gap between the fiber ends, and the surface condition of the fiber end faces. Stability and junction protection are generally functions of the connector design including the material used. For example, a connector generally includes a glass or ceramic cylinder which contains the fiber to the connected, and the end face of which is designed to butt against the end face of a similar cylinder in the mating connector. Such a cylinder is commonly, called a ferrule, and it not only functions to align the core of the fiber, but, also, its end face is sufficiently smooth and flat to insure a uniform butting against the end face of the mating ferrule and, hence, a uniform butting of the fiber end faces.
There are, at present, many different types of connectors in use, all of which are aimed at achieving low insertion loss within the connection, and stability. One such connector is shown in U.S. Pat. No. 4,934,785 of Mathis et al., and comprises a cylindrical ferrule, a base member which holds the ferrule, a compression spring, and a housing surrounding the ferrule and the spring. The ferrule is held rigidly in the housing by suitable adhesive, and the compression spring applies an axial force to the ferrule and housing so that the end face of the ferrule is maintained in contact with the mating ferrule of the second connector. Although such a connector performs its functions well, it has a high parts count assembled in a relatively complex arrangement. A high parts count means a more expensive connector, and, further, the risk of lost parts during assembly, especially in the field. With the increasing use of optical fibers as the transmission media of choice, there is a need for high density interconnect arrangements, hence expensive connectors with a high parts count unduly increase the cost of such interconnection arrangements.
Another type of connector is shown in U.S. Pat. No. 5,481,634 of Anderson et al. and comprises a cylindrical ceramic ferrule contained in a plastic base member to form the fiber holding structure. The fiber holding structure is mounted within a cylindrical housing having an opening therein through which the ferrule protrudes. A cylindrical spring surrounds the base member and interacts with an interior surface of the housing to urge the ferrule axially outward from the housing opening. The housing has a cantilever type spring latch located on one exterior side of the connector which is manually operable and which mates with a shoulder within the receptacle to lock the connector therein. While this particular type of connector lends itself readily to miniaturization, it has a fairly high part count and is, therefore, subject to the same objections as the Mathis et al. connector.
Both of the aforementioned connectors are representative of prior art types, virtually all of which use coil springs to apply the contacting force. In many connectors, the springs also compensate for over-travel. That is, when a connection is made with an LC type connector (Anderson et al.), the ferrule first seats on the optical interface of the mating ferrule (or active device). It is then necessary for the plug housing to continue to advance until the cantilever latch clears the latching shoulder on the receptacle or adapter. The spring absorbs this additional axial advance and once the latch is engaged, the spring, being compressed, continues to apply an axial force between the latch and the plug body to maintain intimate contact at the interface.
There have been connector arrangements aimed at reducing the number of parts in the connector assembly. For example, in U.S. patent application Ser. No. 08/636,451 of Lampert et al., filed Apr. 23, 1996 now U.S. Pat. 5,719,977, there is disclosed a connector having a one-piece molded plastic housing having an exterior cantilever latch. The connector has a cylindrical structure extending toward the front end of the housing which has an axial passage therein for receiving an optical fiber. The cylindrical member is rigidly held within the housing and avoids the use of a spring for applying a contacting force, and the connector is adapted to mate with a conventional connector within an adapter, with the conventional connector having a spring for applying the axial contacting force. Thus, the connector of that application has a very low part count, but relies upon the conventional mating connector to supply the necessary axial contacting force.
Glass optical fibers have, heretofore, been primarily used to bring optical signals to subscriber premises, where they are transformed into electrical signals for distribution throughout the premises. However, there has been a move toward extending the optical signals into and throughout the subscriber premises due to the development of plastic optical fiber (POF). POF has many advantages over glass optical fiber (GOF) for such use. POF is not as brittle as GOF, and does not require extremes of care in handling. POF is less expensive than GOF, thus making it attractive for local usage. Further, POF is not as demanding as glass fiber in alignment because of its larger diameter, hence, the precision ferrule is not a necessary component of the connector. On the other hand, POF has higher signal loss, not having the optical transmissivity of GOF, and hence is preferably used only in short transmission spans, such as within the subscriber premises. It is anticipated that various connections to the several type of apparatus are to be made by the subscriber or customer, hence, the connections will be facilitated by less complicated or sophisticated connectors. Such connections may be made to VCR's, television sets, camcorders, and other types of domestic equipment as well as to telephones, computers, and the like.
Desirably, therefore, an optical connector should have a low part count, reduced size, and should be readily insertable and removable from an associated receptacle without a tool or the need to grasp the opposite sides thereof which is difficult to do when a number of connections are crowded together, while insuring that positive optical contact is made with the mating connector or equipment terminal. In addition, the connector should be of such simplicity that the untrained user, i.e., customers, can readily assemble it.
In the aforementioned U.S. patent application Ser. No. 09/019,242 of A. W. Carlisle et al., there is disclosed a connector that meets the criteria set forth.
The connector of that application and its associated adapter are used for terminating an optical cable or fiber, especially POF, while insuring positive optical contact for optimum signal transmission. The connector plug of the application, in a preferred embodiment thereof, comprises a single molded plastic part having a passage extending axially therethrough. The passage has fiber holding means and a tapered portion extending from the holding means to the rear end of the plug. More particularly, a portion of the passage extending from approximately the middle of the plug toward the rear end has a portion having an enlarged diameter with internal threads, and a second tapered portion extending from the thread portion to the rear end of the plug. The diameter of the threaded portion is such that the threads grip the soft or resilient jacket. With POF, the insulating and protection jacket which surrounds the fiber is bonded to the fiber. Thus, when the jacket is screwed into the threaded portion, the fiber is mounted in the connector, and it is held firmly attached thereto.
A cantilever latch is mounted on (or integral with) the plug adjacent the front end thereof and extends upwardly and rearwardly therefrom. A cantilevered trigger member is affixed to the plug adjacent the rear end thereof and extends upwardly and forwardly of the plug and the front end of the trigger overlies the free end of the cantilever latch. On the top surface of the cantilever latch arm, approximately midway between the ends thereof is a locking tab for locking the latch, and hence the plug, in axial position against rearwardly directed axial forces. On each side of the cantilever latch arm is a radiused camming lobe, extending upwardly and positioned approximately midway between the two ends of the cantilever latch arm.
The receptacle or adapter has an opening therein and an internally extending bore shaped to receive the plug and cantilever latch. The dimensions of the bore are such that when the plug is inserted into the adapter, the cantilever latch arm is depressed until the locking tab passes a shoulder in the bore, at which point the elasticity of the arm causes the locking tab to spring upward to bear against the shoulder and secure the plug against rearward tension. On either side of the shoulder and extending therefrom in a forward direction are first and second sloped or ramped surfaces which slope upwardly toward the operative end of the adapter and against which the radiused camming lobes are adapted to bear when the plug is inserted into the adapter. The natural elasticity of the cantilever latch arm forces the lobes into contact with the ramped surfaces with a resultant downward and forward force being applied through the lobes to the plug. Thus, the lobes tend to move up the slope and the ferrule member is moved forward into contact with the mating coupler or fiber end. The resilience or elasticity of the cantilever latch arm thereby supplies the desired axial contacting force.
Because POF does not require the very precise alignment of the fiber in the connector, it is not necessary to have a precision device such as a ferrule for the fiber at the interface. Thus, the user can achieve sufficient alignment by simply screwing the jacketed fiber into the threaded portion. On the other hand, support means for the fiber end at the interface may be used if desired.
The connector assembly of the application thus has very few parts, is economical to manufacture, is as simple to operate as a standard telephone jack, and makes the use of optical fiber within the subscriber premises plausible and feasible, especially when POF is used.
The plastic cantilever latch arm and associated cam lobes in conjunction with the ramped surface of the adapter provide the needed forward axial contacting force. This contacting force is dependent upon the resilience or elasticity of the latch arm material, i.e., plastic. However, when held in a fixed stressed position, as is the case with the assembled plug and adapter, plastic springs are characterized by a gradual decrease in force with time, a phenomenon known as "creep". As long as some forward force remains creep is not a major concern such as in the case of, for example, a semipermanent connection. On the other hand, in some cases, such as, for example, those where the connection is made and unmade frequently, creep can present problems of nonrepeatability and lack of, or reduced, reliability.